Question

The objects A and B when placed in turn placed in front of concave mirror of focal length 7.5cm ,images of equal in size. If A is three times of size of B is placed 30cm from the mirror. Find the distance of the B from the mirror

Answer 1

Let us consider the simple pendulam makes an angular displacement θ as shown in figure. At this position the forces are weight of the bob of pendulam and Tension acting on the string as shown in figure. Let us resolve the weight mg, the gravitational force into two perpendicular components as shown in figure. one component mgcosθ is in the direction of tension T, that equalize the tension which is giving necessary centripetal force for circular motion. The other perpendicular component mgsinθ is the restoring force acting on the bob to bring to its equilibrium position.